The present invention relates to a two-dimensional optical element array, a two-dimensional waveguide apparatus and methods for manufacturing them. Specifically, this invention relates to a two-dimensional optical element array which is inexpensive and has superior reflection characteristics of end faces, from which light is outgoing or incoming, of optical elements (optical fiber, lens, for example) on a substrate, and can maintain the superior reflection characteristics for a long period and prevent a loss of quantity of light and an adverse effect to another device, a two-dimensional waveguide apparatus having high density and capacity and allowing the number of steps in packaging or connection to be reduced, and efficient methods for manufacturing them.
Recently, with the increased communications data capacity, a demand for an optical cross-connect switch technique that provides a higher throughput of communications data has been increased. For example, there has been used an optical switch that is manufactured using the MEMS (micro-electro-mechanical-system) for conducting fine machining in a semiconductor process including silicon etching, which is used for micro-machining and the like. Besides, with the increased demand for reliability, as well as the demand for the higher throughput, a surface-emitting laser enabling communications with high definition and stability has come into common use.
In such an optical switch or surface-emitting laser, there is used an optical element array (such as, for example optical fiber array, lens array, waveguide array (PLC), semiconductor laser (LD) array, photo diode (PD) array, and the like. Thus, the description will be made, hereinafter, by taking “optical fiber array” as an example of the optical element array). In consideration of requirements for increased throughput and space-saving, the optical fiber array is a so-called two-dimensional optical fiber array (occasionally abbreviated as 2DFA hereinafter) whose cross-section taken along a plane perpendicular to central axes of the aligned optical fibers has a two-dimensional (hierarchical) configuration.
For example, as shown in FIG. 14, there has been proposed a conventional two-dimensional optical fiber array 100 with a pitch in a thickness direction determined by controlling a thickness of a substrate 102 with V-shaped grooves with high precision, arranging optical fibers 101 between the substrates 102 with V-shaped grooves and between the uppermost substrate 102 with V-shaped grooves and the fixing member 103, and stacking the substrates in such a manner that a front surface of each substrate 102 with V-shaped grooves is brought into contact with a back surface of the adjacent substrate 102 with V-shaped groove (for example, JP-A-56-113114).
An optical communication network involving such two-dimensional optical fiber arrays has various connection points therein. If some of the reflected light passing through such connection points is reflected back into the original fiber at time of passing each reflect connection point, a laser or the like is adversely affected (noise occurs, for example).
In particular, in the case of the 2DFA mainly used for the MEMS switch or the like, since lens coupling is often adopted, and a space is provided immediately after the 2DFA. Thus, the degree of the reflection at that point becomes large, and resultantly, the influence caused by light being reflected back into the original fiber again becomes quite serious.
To eliminate the disadvantage described above, in the past, reflection from an end face has been suppressed by providing an AR coating (which is formed by stacking an SiO2 film and a TiO2 film each having a thickness of ¼λ and has a total thickness of the order of a wavelength of light (λ)) on the substrate and an end face, from which light is outgoing or incoming, of the optical element, thereby enhancing reflection characteristics at the end faces.
A waveguide substrate (unit) 205 having one or more waveguides 201 patterned near a surface thereof, shown in FIG. 15, has been used in a splitter, AWG or waveguide modulator, for example. FIG. 15(a) is a schematic plan view of a splitter with one channel input and eight channel outputs, and FIG. 15(b) is a cross-sectional view taken along a line X—X in FIG. 15(a).
However, the conventional two-dimensional optical fiber arrays have problems as described below. The AR coating film is easily degraded by effects of temperature, humidity and other environmental factors and adversely affects the reflection characteristics. Recently, in particular, with the development of the wavelength division multiplex (WDM) communication, the quantity of light transmitted through one optical fiber has been increased, and accordingly, the possibility of a local change in characteristics or local degradation due to the increased quantity of light (light with increased intensity) has been increased. Besides, since the AR coating is provided on the end face of the fiber array when the fibers are mounted thereon, it is difficult to use a vacuum processing for vapor deposition of the AR coating. Thus, multiple AR coatings cannot be conducted at a time, and the cost is increased.
In addition, the above-described waveguide substrate has a problem as follows. When connecting the waveguide substrates and the optical fiber arrays with each other, each of the optical fiber arrays needs to be optically aligned with one of the waveguide substrates. In this alignment, the waveguide substrate and the optical fiber array are aligned with each other on the level of submicrons, and thus, the alignment inevitably requires extremely high precision and many process steps.
The present invention has been devised in view of the above-describe problems, and an object of this invention is to provide an inexpensive two-dimensional optical element array which has superior reflection characteristics of end faces, from which light is outgoing or incoming, of optical elements on a substrate, and can maintain the superior reflection characteristics for a long period and prevent a loss of quantity of light and an adverse effect to another device, a two-dimensional waveguide apparatus having high density and capacity and allowing the number of steps in packaging or connection to be reduced, and efficient methods for manufacturing them.